The victim was identified as Pau Pérez, a Spaniard from Vilafranca del Penedès, 40 miles (64km) from Barcelona.

He was found fatally stabbed in a Ford Focus that had forced its way through a police checkpoint on Thursday, just after a van ploughed into crowds in Barcelona’s Las Ramblas boulevard, killing 13 people.

Police had fired at the car, injuring an officer, and initially thought the man they found in the car had been killed by the gunfire. An investigation revealed he had been stabbed.

Police believe Pérez was stabbed by Younes Abouyaaqoub, a 22-year-old Moroccan national who is alleged to have driven the van along Las Ramblas.

Abouyaaqoub fled the scene of the attack on foot and is thought to have killed Pérez to take his car and escape the city.

Police have set up 800 vehicle checkpoints and tripled the number of officers working on anti-terrorism operations after the attack, but Abouyaaqoub continues to evade them.

El País newspaper published images on Monday of a man it said was Abouyaaqoub apparently making a getaway on foot after the Barcelona van attack. The three photographs show a slim man in sunglasses walking through what El País says is La Boqueria market, just off Las Ramblas.

Describing Abouyaaqoub as about 5ft 11 (1.80 metres), police tweeted four photographs of the man with short black hair, including three pictures in which he was wearing a black and white striped T-shirt. He is “dangerous and could be armed,” police said,

Spain is in three days of mourning for the victims of the attacks, which were claimed by Islamic State. Las Ramblas is filled with about a dozen ever-widening pavement tributes of candles, flowers and messages of sympathy and defiance.

In Seville, anti-Muslim slogans have appeared on a building belonging to a Muslim foundation. In a mass at Valencia Cathedral, Antonio Cañizares, the archbishop of Valencia, warned against “rifts between religions”.

“There is no greater blasphemy than the murder of innocents,” he said. “Islamist jihadism knows nothing but hate – hate for God and for his most beloved creatures, human beings.”